HPV16 E7-dependent transformation activates NHE1 through a PKA-RhoA-induced inhibition of p38alpha.
BACKGROUND
Neoplastic transformation originates from a large number of different genetic alterations. Despite this genetic variability, a common phenotype to transformed cells is cellular alkalinization. We have previously shown in human keratinocytes and a cell line in which transformation can be turned on and followed by the inducible expression of the E7 oncogene of human papillomavirus type 16 (HPV16), that intracellular alkalinization is an early and essential physiological event driven by the up-regulation of the Na/(+)H(+) exchanger isoform 1 (NHE1) and is necessary for the development of other transformed phenotypes and the in vivo tumor formation in nude mice.


METHODS
Here, we utilize these model systems to elucidate the dynamic sequence of alterations of the upstream signal transduction systems leading to the transformation-dependent activation of NHE1.


RESULTS
We observe that a down-regulation of p38 MAPK activity is a fundamental step in the ability of the oncogene to transform the cell. Further, using pharmacological agents and transient transfections with dominant interfering, constitutively active, phosphorylation negative mutants and siRNA strategy to modify specific upstream signal transduction components that link HPV16 E7 oncogenic signals to up-regulation of the NHE1, we demonstrate that the stimulation of NHE1 activity is driven by an early rise in cellular cAMP resulting in the down-stream inhibition of p38 MAPK via the PKA-dependent phosphorylation of the small G-protein, RhoA, and its subsequent inhibition.


CONCLUSIONS
All together these data significantly improve our knowledge concerning the basic cellular alterations involved in oncogene-driven neoplastic transformation.
Cardone
Rosa A
RA
Department of General and Environmental Physiology, University of Bari, Bari, Italy.
Busco
Giovanni
G
Greco
Maria R
MR
Bellizzi
Antonia
A
Accardi
Rosita
R
Cafarelli
Antonella
A
Monterisi
Stefania
S
Carratù
Pierluigi
P
Casavola
Valeria
V
Paradiso
Angelo
A
Tommasino
Massimo
M
Reshkin
Stephan J
SJ
D000818:Animals; D027682:Cation Transport Proteins / Q000378:metabolism*; D002472:Cell Transformation, Viral / Q000235:genetics* / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D015536:Down-Regulation; D015967:Gene Expression Regulation, Viral; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D048308:Mitogen-Activated Protein Kinase 14 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D041681:NIH 3T3 Cells; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013997:Time Factors; D020742:rhoA GTP-Binding Protein / Q000502:physiology*
D027682:Cation Transport Proteins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; C059731:oncogene protein E7, Human papillomavirus type 16; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048308:Mitogen-Activated Protein Kinase 14; D020742:rhoA GTP-Binding Protein